The present invention relates to a display unit displaying desired images by exciting a fluorescent material, and particularly, to a material for improving luminous efficiency and a display unit using the same, which is used, for example, for a gas discharge display unit such as a plasma display panel (hereinafter referred to as PDP).
In a conventional and typical PDP, a gas containing xenon is sealed in space sandwiched between a front substrate and a back substrate. Electric discharge is induced by applying voltage to excite a gas containing xenon, a fluorescent material is excited by emission at a wavelength of 147 nm and by broad emission at a peak wavelength of 170 nm, and desired visible light is generated to display images.
FIG. 7 shows a sectional structure of an AC type plasma display panel, which is an example of the conventional gas discharge display unit. In the figure, numeral 1 is a front glass substrate, numeral 2 is a dielectric material layer, numeral 3 is a protective film, numeral 4 is a discharge gas, numeral 5 is a fluorescent layer, numeral 6 is a partition wall, numeral 7 is a lower layer, numeral 8 is an address electrode, numeral 9 is a back glass substrate, numeral 10 is a sustain discharge electrode, numeral 20 is a dischage cell, numeral 21 is a front panel, and numeral 22 is a back panel.
In the conventional PDP, by applying external voltage to the address electrode 8 and the sustain discharge electrode 10, electric discharge occurs in the discharge cell 20 to excite a discharge gas 4. And at the time when the excited discharge gas 4 is transited to stabilized state, ultraviolet ray is generated (in case of using a xenon gas, it is ray of a wavelength of 147 nm and broad ray at the peak wavelength of 170 nm). By the ultraviolet ray, the fluorescent material layer 5 in the discharge cell 20 is excited to generate visible light necessary for display. And, by using the visible light, desired images are formed and displayed.
However, in these conventional PDP, an energy conversion efficiency (display light/input power) is as low as 0.4%, power consumption is larger than that of CRT or a liquid crystal display unit. And heat is generated as shown, for example, in NIKKEI Electronics, Oct. 25, 1999 (No. 755) p99. Therefore, it has become an important subject to improve the energy conversion efficiency (or luminous efficiency).
In addition, in case of color display of the conventional PDP, balance of luminous intensities of the three kinds of fluorescent materials emitting red, green and blue is important. And it determines a white color temperature at simultaneous emission of the three colors. In the conventional PDP, luminous efficiency of a blue color fluorescent material is poor, and there has been a problem that the white color temperature is low.
With respect to the above problems, at first, as one of the methods for improving the energy conversion efficiency, there is given an effective utilization of ultraviolet ray. In the conventional PDP, the ultraviolet ray irradiated from the discharge gas present in the space of the discharge cell is radiated toward all directions. However, most of the ultraviolet ray directed to the constituting materials surrounding the discharge space excluding the fluorescent material is not utilized for exciting the fluorescent material and it becomes lost. Therefore, it is intended to effectively utilize the ultraviolet ray to improve energy conversion efficiency.
In this respect, there has been a proposal to improve luminous efficiency by utilizing the ultraviolet ray absorbed in the protective film of the dielectric. For example, there is disclosed, as shown in Japanese Unexamined Patent Publication No. 20762/1977, a method for effectively utilizing ultraviolet ray by providing the protective film with fluorescence by containing 1% by weight of CeO in MgO. Also, there is disclosed a method that a fluorescent protective film material (SrMg)2P2O7:Eu2+, which is obtained by mixing the film material with an activator to give fluorescence, absorbs ultraviolet ray generated by gas discharge and discharges ultraviolet ray having a wavelength of 2000 to 3000 xc3x85. However, the wavelength of the ultraviolet ray irradiated according to these methods is at most 300 nm (3000 xc3x85), and thus it was difficult to improve the color temperature as described above.
Also, as a method for improving the color temperature in the conventional PDP, there is, for example, a method for increasing a luminous amount of blue color against the luminous amount of red and green by changing discharging cell width of the three colors to improve the color temperature as disclosed in Japanese Unexamined Patent Publication No. 308179/1998. However, according to this method, since the energy conversion efficiency is not improved and structural conditions of each cell are different, the discharge conditions are different in each cell, and there is a defect that margin of discharge becomes narrow.
In order to solve the above problems, the present inventors performed various experiments. As a result, it was found that by adding a small amount of gadolinium (hereinafter referred to as Gd) among various rare earth elements into a protective film material or the like as a PDP constituted material, the protective film or the like functions as a material for converting ultraviolet ray which generates ultraviolet ray having a longer wavelength on receipt of ultraviolet ray from the discharge gas. And the film improves the luminous efficiency of the display unit such as a plasma display panel, and additionally improves the color temperature of white color display. The present invention is based on these findings.
Japanese Unexamined Patent Publication No. 220640/1995 discloses that the protective film of the alternating current discharge unit contains a compound containing gadolinium. The object of the above method is to obtain a finer magnesium oxide film formed by a printing method to improve sputtering resistance according to discharge, by simultaneously forming a spinal structured Ba0.6Sr0.4Gd2O4 compound containing magnesium oxide and gadolinium according to a printing method. Accordingly, the gadolinium compound is used as a material having adhesive function, and the gadolinium is used only for a partial substituting material of the magnesium oxide film. Furthermore, in the disclosed gadolinium compound, the portion in which gadolinium is locally present has a large gadolinium concentration of about 60% by mole. And there is no generation of long wavelength ultraviolet ray due to concentration quenching (it is thought as a phenomenon caused by absorption of excited energy due to resonance transmission among activator ions when a concentration of the luminous activator added to an oxide is high).
Additionally, it is disclosed, for example, in p120, xe2x80x9cFluorescent Material Handbookxe2x80x9d edited by Fluorescent Material Scientist Academy (published by Ohm Co.) that Gd shows extensive emission at about 315 nm. But there has not been known at all that Gd is used for ultraviolet ray conversion under environment of discharging and exciting fluorescent material.
The present invention has been conducted to solve the problems with the above conventional devices. The object of the present invention is to provide a material for converting ultraviolet ray, which can improve luminous efficiency of a gas discharge display device by utilizing ultraviolet ray otherwise absorbed in a barrier rib, a protective film and the like, and a display device using the same.
The first material for converting ultraviolet ray of the present invention comprises a small amount of gadolinium in a base substrate, wherein ultraviolet ray having the longer wavelength than the irradiated ultraviolet ray is generated by the ultraviolet irradiation.
The second material for converting ultraviolet ray of the present invention is that in the first material, the base substrate comprises an insulating material.
The third material for converting ultraviolet ray of the present invention is that in the first or second material, an amount of the gadolinium is at least 0.1 to at most 20% by mole.
The fourth material for converting ultraviolet ray of the present invention is that in any of the first to third materials, the ultraviolet ray irradiated to the base substrate has a wavelength of at least 200 nm.
The first display device of the present invention comprises a fluorescent material, an exciting means for exciting the fluorescent material and a means for converting ultraviolet ray around the fluorescent material, wherein the means for converting ultraviolet ray contains a small amount of gadolinium in a base substrate and generates, by ultraviolet ray irradiation, ultraviolet ray having a longer wavelength than the irradiated ultraviolet ray.
The second display device of the present invention is that in the first display device, the fluorescent material comprises a plurality of fluorescent materials emitting red light, green light and blue light, wherein the long wavelength ultraviolet ray is irradiated at least to the fluorescent material emitting blue light.
The third display device of the present invention is that in any of the first and second display device, an amount of the gadolinium is at least 0.1 to at most 20% by mole.
The fourth display device of the present invention is that in any of the first to third display device, a wavelength of the ultraviolet ray irradiated to the base substrate is at most 200 nm.
The fifth display device of the present invention comprises a first substrate having a dielectric and a protective film for protecting the dielectric; a second substrate having a partition wall and a fluorescent material layer and opposing to the first substrate; a rare gas filling space held between the first substrate and the second substrate; and an exciting means for exciting the fluorescent material layer by discharge of the rare gas and controlling lighting of a plurality of pixels, wherein at least one of the dielectric, the protective film and the partition wall contains a small amount of gadolinium.
The sixth display device of the present invention is that in the fifth display device, the protective film comprises MgO containing a small amount of gadolinium.
The seventh display device of the present invention is that in the fifth or the sixth display device, the fluorescent material layer comprises a plurality of fluorescent material layers, which are parted by the partition wall and emit red, green and blue light.
The eighth display device of the present invention is that in any of fifth to seventh display device, the first ultraviolet ray is generated by discharge of the rare gas to excite the gadolinium, leading to the generation of the second ultraviolet ray having a longer wavelength than that of the first ultraviolet ray.
The ninth display device of the present invention is that in the eighth display device, a white color temperature is controlled due to increase of luminous intensity of the fluorescent material layer emitting blue light by the second ultraviolet ray.
The tenth display device of the present invention is that in any of the fifth to ninth device, an amount of the gadolinium is at least 0.1 to at most 20% by mole.
The eleventh display device of the present invention is that in any of the eighth to tenth display device, a wavelength of the first ultraviolet ray is at most 200 nm.
The twelfth display device of the present invention is that in any of the eighth to eleventh display device, the fluorescent material layer has two-layered structure of the first fluorescent material layer and the second fluorescent material layer, wherein the white color temperature is controlled by setting the first ultraviolet ray and the second ultraviolet ray to the pre-determined values and by adjusting luminous intensities of the first and second fluorescent material layers.
The thirteenth display device of the present invention is that in twelfth display device, the first fluorescent material layer is formed on the second fluorescent material layer.
The fourteenth display device of the present invention is that in any of the twelfth and thirteenth display device, the first fluorescent material layer is thinner than the second fluorescent material layer.
The fifteenth display device of the present invention is that in sixth display device, an amount of the gadolinium is at least 0.1 to at most 20% by mole.